(a) Field of the Invention
This invention relates to liquid-filled anti-vibration mounting device used, for example, in motor vehicles, and particularly relates to the structure for restraining the production of abnormal noise due to abutment of a movable plate against a partition member in a liquid-filled anti-vibration mounting device in which the movable plate is contained in the partition member in a liquid chamber.
(b) Description of the Related Art
An example of known liquid-filled anti-vibration mounting devices of such kind is an engine mount for a motor vehicle. The engine mount has a basic structure in which a rubber elastic material is interposed between a mounting member for an engine and a support member for a vehicle body, a liquid chamber is formed between both the members to change its volume with deformation of the rubber elastic material and partitioned into a pressure receiving chamber and a balancing chamber and an orifice passage is provided for communicating the pressure receiving chamber with the balancing chamber.
The orifice passage is tuned to relatively low-frequency and large-amplitude vibrations, such as vibrations at engine start-up, jerky vibrations at gear change or shaking, and such vibrations to be input to the engine mount can be effectively damped by a resonance (liquid column resonance) generated when the liquid flows via the orifice passage between the pressure receiving chamber and the balancing chamber.
The partition member partitioning the liquid chamber into the pressure receiving chamber and the balancing chamber is composed of a pair of division walls disposed with a specified distance between them, one division wall adjoining the pressure receiving chamber and the other adjoining the balancing chamber. An accommodation room containing a movable plate is defined between the pair of division walls. The pair of division walls are each formed with communication holes, the communication holes in one of the division walls communicate the accommodation room with the pressure receiving chamber and the communication holes in the other division wall communicate the accommodation room with the balancing chamber. When a change in the liquid pressure in the liquid chamber is transmitted via the communication holes to the accommodation room, the movable plate moves to absorb the change.
Specifically, when vibrations are input to the engine mount with such a relatively high frequency and a small amplitude that the orifice passage may be clogged, changes in the liquid pressure in the pressure receiving chamber due to the vibrations are transmitted via the communication holes in the associated division wall to the accommodation room and the movable plate in the accommodation room vibrates in synchronization with the changes in the liquid pressure to absorb the changes. On the other hand, when relatively low-frequency and large-amplitude vibrations are input to the engine mount as described above, the movable plate responding to changes in liquid pressure due to the vibrations is pressed against the associated division wall to close the communication holes.
When the movable plate moves in the accommodation room in the partition member as described above, a shock occurs upon abutment against the division wall and is transmitted to the vehicle body, which may produce abnormal noise in the passenger compartment. Such abnormal noise, though its magnitude differs depending upon the vibration transmission characteristics of the vehicle body, can be reduced by lessening the shock.
To attain this, for example, in an engine mount disclosed in Published Japanese Patent Application No. 2006-38016, each surface of the movable plate is formed with a large number of dimples so that upon abutment against the facing division wall (referred to as the top plate or the bottom plate in the document), voids can be locally created by the dimples. Thus, the contact area of the movable plate with the division wall can be reduced to lessen a shock due to the abutment.
In another engine mount disclosed in Published Japanese Patent Application No. 2006-207630, a set of communication holes (referred to as slot openings in the document) in each division wall are offset in a radial direction, or towards a lateral side, with respect to the center of the movable plate. When a liquid pressure acts through the communication holes on the movable plate, the movable plate is radially inclined and thereby brought into gradual contact with the division wall with its lateral side end first and the rest delayed. Thus, the shock due to the contact can be dispersed in a time-shared manner and thereby eased.